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Chiu LY, Emery A, Jain N, Sugarman A, Kendrick N, Luo L, Ford W, Swanstrom R, Tolbert BS. Encoded Conformational Dynamics of the HIV Splice Site A3 Regulatory Locus: Implications for Differential Binding of hnRNP Splicing Auxiliary Factors. J Mol Biol 2022; 434:167728. [PMID: 35870649 PMCID: PMC9945881 DOI: 10.1016/j.jmb.2022.167728] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2022] [Revised: 07/07/2022] [Accepted: 07/07/2022] [Indexed: 01/19/2023]
Abstract
Alternative splicing of the HIV transcriptome is controlled through cis regulatory elements functioning as enhancers or silencers depending on their context and the type of host RNA binding proteins they recruit. Splice site acceptor A3 (ssA3) is one of the least used acceptor sites in the HIV transcriptome and its activity determines the levels of tat mRNA. Splice acceptor 3 is regulated by a combination of cis regulatory sequences, auxiliary splicing factors, and presumably RNA structure. The mechanisms by which these multiple regulatory components coordinate to determine the frequency in which ssA3 is utilized is poorly understood. By NMR spectroscopy and phylogenetic analysis, we show that the ssA3 regulatory locus is conformationally heterogeneous and that the sequences that encompass the locus are conserved across most HIV isolates. Despite the conformational heterogeneity, the major stem loop (A3SL1) observed in vitro folds to base pair the Polypyrimdine Tract (PPyT) to the Exon Splicing Silencer 2p (ESS2p) element and to a conserved downstream linker. The 3D structure as determined by NMR spectroscopy further reveals that the A3 consensus cleavage site is embedded within a unique stereochemical environment within the apical loop, where it is surrounded by alternating base-base interactions. Despite being described as a receptor for hnRNP H, the ESS2p element is sequestered by base pairing to the 3' end of the PPyT and within this context it cannot form a stable complex with hnRNP H. By comparison, hnRNP A1 directly binds to the A3 consensus cleavage site located within the apical loop, suggesting that it can directly modulate U2AF assembly. Sequence mutations designed to destabilize the PPyT:ESS2p helix results in an increase usage of ssA3 within HIV-infected cells, consistent with the PPyT becoming more accessible for U2AF recognition. Additional mutations introduced into the downstream ESS2 element synergize with ESS2p to cause further increases in ssA3 usage. When taken together, our work provides a unifying picture by which cis regulatory sequences, splicing auxiliary factors and RNA structure cooperate to provide stringent control over ssA3. We describe this as the pair-and-lock mechanism to restrict access of the PPyT, and posit that it operates to regulate a subset of the heterogenous structures encompassing the ssA3 regulatory locus.
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Affiliation(s)
- Liang-Yuan Chiu
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States. https://twitter.com/LiangYuanChiu1
| | - Ann Emery
- UNC Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, United States
| | - Niyati Jain
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States
| | - Andrew Sugarman
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States. https://twitter.com/sugarman_andrew
| | - Nashea Kendrick
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States
| | - Le Luo
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States
| | - William Ford
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States
| | - Ronald Swanstrom
- UNC Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, United States; Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, United States; Center for AIDS Research, University of North Carolina, Chapel Hill, NC 27599, United States
| | - Blanton S Tolbert
- Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, United States.
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Lee MYH, Khoury G, Olshansky M, Sonza S, Carter GP, McMahon J, Stinear TP, Turner SJ, Lewin SR, Purcell DFJ. Detection of Chimeric Cellular: HIV mRNAs Generated Through Aberrant Splicing in HIV-1 Latently Infected Resting CD4+ T Cells. Front Cell Infect Microbiol 2022; 12:855290. [PMID: 35573784 PMCID: PMC9096486 DOI: 10.3389/fcimb.2022.855290] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Accepted: 03/25/2022] [Indexed: 11/13/2022] Open
Abstract
Latent HIV-1 provirus in infected individuals on suppressive therapy does not always remain transcriptionally silent. Both HIV-1 LTR and human gene promoter derived transcriptional events can contribute HIV-1 sequences to the mRNA produced in the cell. In addition, chimeric cellular:HIV mRNA can arise through readthrough transcription and aberrant splicing. Using target enrichment coupled to the Illumina Mi-Seq and PacBio RS II platforms, we show that 3’ LTR activation is frequent in latently infected cells from both the CCL19-induced primary cell model of HIV-1 latency as well as ex vivo samples. In both systems of latent HIV-1 infection, we detected several chimeric species that were generated via activation of a cryptic splice donor site in the 5’ LTR of HIV-1. Aberrant splicing involving the major HIV-1 splice donor sites, SD1 and SD4 disrupts post-transcriptional processing of the gene in which HIV-1 is integrated. In the primary cell model of HIV-1 latency, Tat-encoding sequences are incorporated into the chimeric mRNA transcripts through the use of SD4. Our study unravels clues to the characteristics of HIV-1 integrants that promote formation of chimeric cellular:HIV mRNA and improves the understanding of the HIV-1 RNA footprint in latently infected cells.
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Affiliation(s)
- Michelle Y-H Lee
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Georges Khoury
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Moshe Olshansky
- Department of Microbiology, Biomedical Discovery Institute, Monash University, Melbourne, VIC, Australia
| | - Secondo Sonza
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Glen P. Carter
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
- Doherty Applied Microbial Genomics, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - James McMahon
- Department of Infectious Diseases, Monash University and Alfred Hospital, Melbourne, VIC, Australia
| | - Timothy P. Stinear
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
- Doherty Applied Microbial Genomics, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Stephen J. Turner
- Department of Microbiology, Biomedical Discovery Institute, Monash University, Melbourne, VIC, Australia
| | - Sharon R. Lewin
- Department of Infectious Diseases, Monash University and Alfred Hospital, Melbourne, VIC, Australia
- Department of Infectious Diseases, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
- Victorian Infectious Diseases Service, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
| | - Damian F. J. Purcell
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia
- *Correspondence: Damian F. J. Purcell,
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Sharma S, Arunachalam PS, Menon M, Ragupathy V, Satya RV, Jebaraj J, Aralaguppe SG, Rao C, Pal S, Saravanan S, Murugavel KG, Balakrishnan P, Solomon S, Hewlett I, Ranga U. PTAP motif duplication in the p6 Gag protein confers a replication advantage on HIV-1 subtype C. J Biol Chem 2018; 293:11687-11708. [PMID: 29773649 DOI: 10.1074/jbc.m117.815829] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2017] [Revised: 04/30/2018] [Indexed: 11/06/2022] Open
Abstract
HIV-1 subtype C (HIV-1C) may duplicate longer amino acid stretches in the p6 Gag protein, leading to the creation of an additional Pro-Thr/Ser-Ala-Pro (PTAP) motif necessary for viral packaging. However, the biological significance of a duplication of the PTAP motif for HIV-1 replication and pathogenesis has not been experimentally validated. In a longitudinal study of two different clinical cohorts of select HIV-1 seropositive, drug-naive individuals from India, we found that 8 of 50 of these individuals harbored a mixed infection of viral strains discordant for the PTAP duplication. Conventional and next-generation sequencing of six primary viral quasispecies at multiple time points disclosed that in a mixed infection, the viral strains containing the PTAP duplication dominated the infection. The dominance of the double-PTAP viral strains over a genetically similar single-PTAP viral clone was confirmed in viral proliferation and pairwise competition assays. Of note, in the proximity ligation assay, double-PTAP Gag proteins exhibited a significantly enhanced interaction with the host protein tumor susceptibility gene 101 (Tsg101). Moreover, Tsg101 overexpression resulted in a biphasic effect on HIV-1C proliferation, an enhanced effect at low concentration and an inhibitory effect only at higher concentrations, unlike a uniformly inhibitory effect on subtype B strains. In summary, our results indicate that the duplication of the PTAP motif in the p6 Gag protein enhances the replication fitness of HIV-1C by engaging the Tsg101 host protein with a higher affinity. Our results have implications for HIV-1 pathogenesis, especially of HIV-1C.
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Affiliation(s)
- Shilpee Sharma
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | - Prabhu S Arunachalam
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | - Malini Menon
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | - Viswanath Ragupathy
- the Laboratory of Molecular Virology, Division of Emerging and Transmission Transmitted Diseases, Office of Blood Review and Research, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993
| | | | - Joshua Jebaraj
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | | | - Chaitra Rao
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | - Sreshtha Pal
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India
| | - Shanmugam Saravanan
- the Y. R. Gaitonde Centre for AIDS Research and Education, Chennai 600113, India
| | | | | | - Suniti Solomon
- the Y. R. Gaitonde Centre for AIDS Research and Education, Chennai 600113, India
| | - Indira Hewlett
- the Laboratory of Molecular Virology, Division of Emerging and Transmission Transmitted Diseases, Office of Blood Review and Research, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993
| | - Udaykumar Ranga
- From the Jawaharlal Nehru Centre for Advanced Scientific Research, HIV-AIDS Laboratory, Bengaluru 56006, India,
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Vega Y, Delgado E, de la Barrera J, Carrera C, Zaballos Á, Cuesta I, Mariño A, Ocampo A, Miralles C, Pérez-Castro S, Álvarez H, López-Miragaya I, García-Bodas E, Díez-Fuertes F, Thomson MM. Sequence Analysis of In Vivo-Expressed HIV-1 Spliced RNAs Reveals the Usage of New and Unusual Splice Sites by Viruses of Different Subtypes. PLoS One 2016; 11:e0158525. [PMID: 27355361 PMCID: PMC4927154 DOI: 10.1371/journal.pone.0158525] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 06/16/2016] [Indexed: 11/18/2022] Open
Abstract
HIV-1 RNAs are generated through a complex splicing mechanism, resulting in a great diversity of transcripts, which are classified in three major categories: unspliced, singly spliced (SS), and doubly spliced (DS). Knowledge on HIV-1 RNA splicing in vivo and by non-subtype B viruses is scarce. Here we analyze HIV-1 RNA splice site usage in CD4+CD25+ lymphocytes from HIV-1-infected individuals through pyrosequencing. HIV-1 DS and SS RNAs were amplified by RT-PCR in 19 and 12 samples, respectively. 13,108 sequences from HIV-1 spliced RNAs, derived from viruses of five subtypes (A, B, C, F, G), were identified. In four samples, three of non-B subtypes, five 3' splice sites (3'ss) mapping to unreported positions in the HIV-1 genome were identified. Two, designated A4i and A4j, were used in 22% and 25% of rev RNAs in two viruses of subtypes B and A, respectively. Given their close proximity (one or two nucleotides) to A4c and A4d, respectively, they could be viewed as variants of these sites. Three 3'ss, designated A7g, A7h, and A7i, located 20, 32, and 18 nucleotides downstream of A7, respectively, were identified in a subtype C (A7g, A7h) and a subtype G (A7i) viruses, each in around 2% of nef RNAs. The new splice sites or variants of splice sites were associated with the usual sequence features of 3'ss. Usage of unusual 3'ss A4d, A4e, A5a, A7a, and A7b was also detected. A4f, previously identified in two subtype C viruses, was preferentially used by rev RNAs of a subtype C virus. These results highlight the great diversity of in vivo splice site usage by HIV-1 RNAs. The fact that four of five newly identified splice sites or variants of splice sites were detected in non-subtype B viruses allows anticipating an even greater diversity of HIV-1 splice site usage than currently known.
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Affiliation(s)
- Yolanda Vega
- HIV Biology and Variability Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Elena Delgado
- HIV Biology and Variability Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Jorge de la Barrera
- Bioinformatics Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Cristina Carrera
- HIV Biology and Variability Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Ángel Zaballos
- Genomics Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Isabel Cuesta
- Bioinformatics Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Ana Mariño
- Hospital Arquitecto Marcide. Ferrol, A Coruña, Spain
| | - Antonio Ocampo
- Complejo Hospitalario Universitario de Vigo. Vigo, Pontevedra, Spain
| | - Celia Miralles
- Complejo Hospitalario Universitario de Vigo. Vigo, Pontevedra, Spain
| | | | | | | | - Elena García-Bodas
- HIV Biology and Variability Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Francisco Díez-Fuertes
- AIDS Immunopathogenesis Unit. Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
| | - Michael M. Thomson
- HIV Biology and Variability Unit, Centro Nacional de Microbiología, Instituto de Salud Carlos III. Majadahonda, Madrid, Spain
- * E-mail:
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Vega Y, Delgado E, Carrera C, Nebreda P, Fernández-García A, Cuevas MT, Pérez-Álvarez L, Thomson MM. Identification of new and unusual rev and nef transcripts expressed by an HIV type 1 primary isolate. AIDS Res Hum Retroviruses 2013; 29:1075-8. [PMID: 23540799 DOI: 10.1089/aid.2013.0053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
We analyzed RNA splice site usage in three HIV-1 subtype B primary isolates through reverse transcriptase polymerase chain reaction (RT-PCR) amplification of spliced RNAs using a fluorescently labeled primer, with computerized size determination and quantification of PCR products, which were also identified by clone sequencing. In one isolate, P2149-3, unusual and unreported spliced transcripts were detected. This isolate preferentially used for rev RNA generation a 3' splice site (3'ss) located five nucleotides upstream of A4a, previously identified only in a T cell line-adapted virus and in a group O isolate, and designated A4d. P2149-3 also used an unreported 3'ss for rev RNA generation, designated A4h, located 20 nucleotides upstream of 3'ss A4c. Additionally, unusual nef RNAs using 3'ss A5a and A7a and with exon composition 1.3.7 were identified. The identification of several unusual and unreported spliced transcripts in an HIV-1 primary isolate suggests a greater diversity of splice site usage in HIV-1 than previously appreciated.
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Affiliation(s)
- Yolanda Vega
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Elena Delgado
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Cristina Carrera
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Paloma Nebreda
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | | | - María Teresa Cuevas
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Lucía Pérez-Álvarez
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Michael M. Thomson
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
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Li GH, Li W, Mumper RJ, Nath A. Molecular mechanisms in the dramatic enhancement of HIV-1 Tat transduction by cationic liposomes. FASEB J 2012; 26:2824-34. [PMID: 22447980 DOI: 10.1096/fj.11-203315] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat) protein possesses a unique membrane-transduction property. Interestingly, Tat transduction could be dramatically increased 1000-fold based on LTR-transactivation assay when complexed with cationic liposomes (lipo-Tat), compared with Tat alone. Therefore, underlining mechanisms were explored further. Microscopy and flow cytometry showed that this effect was associated with enhanced membrane binding, large particle formation (1-2 μm) and increased intracellular uptake of Tat fluorescent proteins. Using pharmacological assays and immune colocalizations, it was found that lipid raft-dependent endocytosis and macropinocytosis were major pathways involved in lipo-Tat uptake, and actin-filaments played a major role in intracellular trafficking of lipo-Tat to the nucleus. Furthermore, we found that the Tat hydrophobic domain (aa 36-47) mediated formation of two positively charged molecules into lipo-Tat complexes via hydrophobic bonds, based on LTR-transactivation inhibition assay. Thus, the hydrophobic domain may play an important role in Tat protein uptake and be useful for intracellular delivery of biomacromolecules if coupled together with Tat basic peptide, a cell-penetrating peptide.
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Affiliation(s)
- Guan-Han Li
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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7
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Delgado E, Carrera C, Nebreda P, Fernández-García A, Pinilla M, García V, Pérez-Álvarez L, Thomson MM. Identification of new splice sites used for generation of rev transcripts in human immunodeficiency virus type 1 subtype C primary isolates. PLoS One 2012; 7:e30574. [PMID: 22363449 PMCID: PMC3281843 DOI: 10.1371/journal.pone.0030574] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Accepted: 12/21/2011] [Indexed: 12/16/2022] Open
Abstract
The HIV-1 primary transcript undergoes a complex splicing process by which more than 40 different spliced RNAs are generated. One of the factors contributing to HIV-1 splicing complexity is the multiplicity of 3′ splice sites (3'ss) used for generation of rev RNAs, with two 3'ss, A4a and A4b, being most commonly used, a third site, A4c, used less frequently, and two additional sites, A4d and A4e, reported in only two and one isolates, respectively. HIV-1 splicing has been analyzed mostly in subtype B isolates, and data on other group M clades are lacking. Here we examine splice site usage in three primary isolates of subtype C, the most prevalent clade in the HIV-1 pandemic, by using an in vitro infection assay of peripheral blood mononuclear cells. Viral spliced RNAs were identified by RT-PCR amplification using a fluorescently-labeled primer and software analyses and by cloning and sequencing the amplified products. The results revealed that splice site usage for generation of rev transcripts in subtype C differs from that reported for subtype B, with most rev RNAs using two previously unreported 3'ss, one located 7 nucleotides upstream of 3'ss A4a, designated A4f, preferentially used by two isolates, and another located 14 nucleotides upstream of 3'ss A4c, designated A4g, preferentially used by the third isolate. A new 5′ splice site, designated D2a, was also identified in one virus. Usage of the newly identified splice sites is consistent with sequence features commonly found in subtype C viruses. These results show that splice site usage may differ between HIV-1 subtypes.
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Affiliation(s)
- Elena Delgado
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Cristina Carrera
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Paloma Nebreda
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | | | - Milagros Pinilla
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Valentina García
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Lucía Pérez-Álvarez
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Michael M. Thomson
- Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- * E-mail:
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Abstract
Over 40 different human immunodeficiency virus type 1 (HIV-1) mRNA species, both completely and incompletely spliced, are produced by alternative splicing of the primary viral RNA transcript. In addition, about half of the viral RNA remains unspliced and is transported to the cytoplasm where it is used both as mRNA and as genomic RNA. In general, the identities of the completely and incompletely spliced HIV-1 mRNA species are determined by the proximity of the open reading frames to the 5'-end of the mRNAs. The relative abundance of the mRNAs encoding the HIV-1 gene products is determined by the frequency of splicing at the different alternative 3'-splice sites. This chapter will highlight studies showing how HIV-1 uses exon definition to control the level of splicing at each of its 3'-splice sites through a combination of positively acting exonic splicing enhancer (ESE) elements, negatively acting exonic and intronic splicing silencer elements (ESS and ISS elements, respectively), and the 5'-splice sites of the regulated exons. Each of these splicing elements represent binding sites for cellular factors whose levels in the infected cell can determine the dominance of the positive or negative elements on HIV-1 alternative splicing. Both mutations of HIV-1 splicing elements and overexpression or inhibition of cellular splicing factors that bind to these elements have been used to show that disruption of regulated splicing inhibits HIV-1 replication. These studies have provided strong rationale for the investigation and development of antiviral drugs that specifically inhibit HIV-1 RNA splicing.
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Lichtenberg J, Yilmaz A, Welch JD, Kurz K, Liang X, Drews F, Ecker K, Lee SS, Geisler M, Grotewold E, Welch LR. The word landscape of the non-coding segments of the Arabidopsis thaliana genome. BMC Genomics 2009; 10:463. [PMID: 19814816 PMCID: PMC2770528 DOI: 10.1186/1471-2164-10-463] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Accepted: 10/08/2009] [Indexed: 11/23/2022] Open
Abstract
Background Genome sequences can be conceptualized as arrangements of motifs or words. The frequencies and positional distributions of these words within particular non-coding genomic segments provide important insights into how the words function in processes such as mRNA stability and regulation of gene expression. Results Using an enumerative word discovery approach, we investigated the frequencies and positional distributions of all 65,536 different 8-letter words in the genome of Arabidopsis thaliana. Focusing on promoter regions, introns, and 3' and 5' untranslated regions (3'UTRs and 5'UTRs), we compared word frequencies in these segments to genome-wide frequencies. The statistically interesting words in each segment were clustered with similar words to generate motif logos. We investigated whether words were clustered at particular locations or were distributed randomly within each genomic segment, and we classified the words using gene expression information from public repositories. Finally, we investigated whether particular sets of words appeared together more frequently than others. Conclusion Our studies provide a detailed view of the word composition of several segments of the non-coding portion of the Arabidopsis genome. Each segment contains a unique word-based signature. The respective signatures consist of the sets of enriched words, 'unwords', and word pairs within a segment, as well as the preferential locations and functional classifications for the signature words. Additionally, the positional distributions of enriched words within the segments highlight possible functional elements, and the co-associations of words in promoter regions likely represent the formation of higher order regulatory modules. This work is an important step toward fully cataloguing the functional elements of the Arabidopsis genome.
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Affiliation(s)
- Jens Lichtenberg
- Bioinformatics Laboratory, School of Electrical Engineering and Computer Science, Ohio University, Athens, OH, USA.
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10
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Role of Tat protein in HIV neuropathogenesis. Neurotox Res 2009; 16:205-20. [PMID: 19526283 DOI: 10.1007/s12640-009-9047-8] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 03/09/2009] [Accepted: 03/09/2009] [Indexed: 12/13/2022]
Abstract
The Tat protein of the human immunodeficiency virus (HIV) has been implicated in the pathophysiology of the neurocognitive deficits associated with HIV infection. This is the earliest protein to be produced by the proviral DNA in the infected cell. The protein not only drives the regulatory regions of the virus but may also be actively released from the cell and then interact with the cell surface receptors of other uninfected cells in the brain leading to cellular dysfunction. It may also be taken up by these cells and can then activate a number of host genes. The Tat protein is highly potent and has the unique ability to travel along neuronal pathways. Importantly, its production is not impacted by the use of antiretroviral drugs once the proviral DNA has been formed. This article reviews the pleomorphic actions of Tat protein and the evidence supporting its central role in the neuropathogenesis of the HIV infection.
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Schaub MC, Lopez SR, Caputi M. Members of the heterogeneous nuclear ribonucleoprotein H family activate splicing of an HIV-1 splicing substrate by promoting formation of ATP-dependent spliceosomal complexes. J Biol Chem 2007; 282:13617-26. [PMID: 17337441 DOI: 10.1074/jbc.m700774200] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study we analyzed members of the heterogeneous nuclear ribonucleoprotein (hnRNP) H protein family to determine their RNA binding specificities and roles in splicing regulation. Our data indicate that hnRNPs H, H', F, 2H9, and GRSF-1 bind the consensus motif DGGGD (where D is U, G, or A) and aggregate in a multimeric complex. We analyzed the role of these proteins in the splicing of a substrate derived from the HIV-1 tat gene and have shown that hnRNP H family members are required for efficient splicing of this substrate. The hnRNP H protein family members activated splicing of the viral substrate by promoting the formation of ATP-dependent spliceosomal complexes. Mutational analysis of six consensus motifs present within the intron of the substrate indicated that only one of these motifs acts as an intronic splicing enhancer.
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Affiliation(s)
- Michael C Schaub
- Department of Biomedical Science, Florida Atlantic University, Boca Raton, Florida 33431, USA
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Kammler S, Otte M, Hauber I, Kjems J, Hauber J, Schaal H. The strength of the HIV-1 3' splice sites affects Rev function. Retrovirology 2006; 3:89. [PMID: 17144911 PMCID: PMC1697824 DOI: 10.1186/1742-4690-3-89] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 12/04/2006] [Indexed: 11/16/2022] Open
Abstract
Background The HIV-1 Rev protein is a key component in the early to late switch in HIV-1 splicing from early intronless (e.g. tat, rev) to late intron-containing Rev-dependent (e.g. gag, vif, env) transcripts. Previous results suggested that cis-acting sequences and inefficient 5' and 3' splice sites are a prerequisite for Rev function. However, we and other groups have shown that two of the HIV-1 5' splice sites, D1 and D4, are efficiently used in vitro and in vivo. Here, we focus on the efficiency of the HIV-1 3' splice sites taking into consideration to what extent their intrinsic efficiencies are modulated by their downstream cis-acting exonic sequences. Furthermore, we delineate their role in RNA stabilization and Rev function. Results In the presence of an efficient upstream 5' splice site the integrity of the 3' splice site is not essential for Rev function whereas an efficient 3' splice site impairs Rev function. The detrimental effect of a strong 3' splice site on the amount of Rev-dependent intron-containing HIV-1 glycoprotein coding (env) mRNA is not compensatable by weakening the strength of the upstream 5' splice site. Swapping the HIV-1 3' splice sites in an RRE-containing minigene, we found a 3' splice site usage which was variably dependent on the presence of the usual downstream exonic sequence. The most evident activation of 3' splice site usage by its usual downstream exonic sequence was observed for 3' splice site A1 which was turned from an intrinsic very weak 3' splice site into the most active 3' splice site, even abolishing Rev activity. Performing pull-down experiments with nuclear extracts of HeLa cells we identified a novel ASF/SF2-dependent exonic splicing enhancer (ESE) within HIV-1 exon 2 consisting of a heptameric sequence motif occurring twice (M1 and M2) within this short non-coding leader exon. Single point mutation of M1 within an infectious molecular clone is detrimental for HIV-1 exon 2 recognition without affecting Rev-dependent vif expression. Conclusion Under the conditions of our assay, the rate limiting step of retroviral splicing, competing with Rev function, seems to be exclusively determined by the functional strength of the 3' splice site. The bipartite ASF/SF2-dependent ESE within HIV-1 exon 2 supports cross-talk between splice site pairs across exon 2 (exon definition) which is incompatible with processing of the intron-containing vif mRNA. We propose that Rev mediates a switch from exon to intron definition necessary for the expression of all intron-containing mRNAs.
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Affiliation(s)
- Susanne Kammler
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Allé, Bldg. 1130, DK-8000 Aarhus C, Denmark
| | - Marianne Otte
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
- Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 26.03, D-40225 Düsseldorf, Germany
| | - Ilona Hauber
- Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, D-20251 Hamburg, Germany
| | - Jørgen Kjems
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Allé, Bldg. 1130, DK-8000 Aarhus C, Denmark
| | - Joachim Hauber
- Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, D-20251 Hamburg, Germany
| | - Heiner Schaal
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
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Hallay H, Locker N, Ayadi L, Ropers D, Guittet E, Branlant C. Biochemical and NMR Study on the Competition between Proteins SC35, SRp40, and Heterogeneous Nuclear Ribonucleoprotein A1 at the HIV-1 Tat Exon 2 Splicing Site. J Biol Chem 2006; 281:37159-74. [PMID: 16990281 DOI: 10.1074/jbc.m603864200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human immunodeficiency virus, type 1, Tat protein plays a key role in virus multiplication. Because of its apoptotic property, its production is highly controlled. It depends upon the A3 splicing site utilization. A key control of site A3 activity is the ESS2 splicing silencer, which is located within the long stem-loop structure 3 (SLS3), far downstream from site A3. Here, by enzymatic footprints, we demonstrate the presence of several heterogeneous nuclear ribonucleoprotein (hnRNP) A1-binding sites on SLS3 and show the importance of the C-terminal Gly domain of hnRNP A1 in the formation of stable complexes containing several hnRNP A1 molecules bound on SLS3. Mutations in each of the UAG triplets in ESS2 strongly reduce the overall hnRNP A1 binding, showing the central role of ESS2 in hnRNP A1 assembly on SLS2-SLS3. Using NMR spectroscopy, we demonstrate the direct interaction of ESS2 with the RNA recognition motifs domains of hnRNP A1. This interaction has limited effect on the RNA two-dimensional structure. The SR proteins SC35 and SRp40 were found previously to be strong activators of site A3 utilization. By enzymatic and chemical footprints, we delineate their respective binding sites on SLS2 and SLS3 and find a strong similarity between the hnRNP A1-, SC35-, and SRp40-binding sites. The strongest SC35-binding site only has a modest contribution to site A3 activation. Hence, the main role of SR proteins at site A3 is to counteract hnRNP A1 binding on ESS2 and ESE2. Indeed, we found that ESE2 has inhibitory properties because of its ability to bind hnRNP A1.
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Affiliation(s)
- Houda Hallay
- UMR 7567 CNRS-Université Henri Poincaré-Nancy I, Boulevard des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy Cedex and Laboratoire de Chimie et Biologie Structurales, ICSN-CNRS, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France
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14
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Madsen JM, Stoltzfus CM. A suboptimal 5' splice site downstream of HIV-1 splice site A1 is required for unspliced viral mRNA accumulation and efficient virus replication. Retrovirology 2006; 3:10. [PMID: 16457729 PMCID: PMC1403798 DOI: 10.1186/1742-4690-3-10] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Accepted: 02/03/2006] [Indexed: 11/10/2022] Open
Abstract
Background Inefficient alternative splicing of the human immunodeficiency virus type 1(HIV-1) primary RNA transcript results in greater than half of all viral mRNA remaining unspliced. Regulation of HIV-1 alternative splicing occurs through the presence of suboptimal viral 5' and 3' splice sites (5' and 3'ss), which are positively regulated by exonic splicing enhancers (ESE) and negatively regulated by exonic splicing silencers (ESS) and intronic splicing silencers (ISS). We previously showed that splicing at HIV-1 3'ss A2 is repressed by ESSV and enhanced by the downstream 5'ss D3 signal. Disruption of ESSV results in increased vpr mRNA accumulation and exon 3 inclusion, decreased accumulation of unspliced viral mRNA, and decreased virus production. Results Here we show that optimization of the 5'ss D2 signal results in increased splicing at the upstream 3'ss A1, increased inclusion of exon 2 into viral mRNA, decreased accumulation of unspliced viral mRNA, and decreased virus production. Virus production from the 5'ss D2 and ESSV mutants was rescued by transient expression of HIV-1 Gag and Pol. We further show that the increased inclusion of either exon 2 or 3 does not significantly affect the stability of viral mRNA but does result in an increase and decrease, respectively, in HIV-1 mRNA levels. The changes in viral mRNA levels directly correlate with changes in tat mRNA levels observed upon increased inclusion of exon 2 or 3. Conclusion These results demonstrate that splicing at HIV-1 3'ss A1 is regulated by the strength of the downstream 5'ss signal and that suboptimal splicing at 3'ss A1 is necessary for virus replication. Furthermore, the replication defective phenotype resulting from increased splicing at 3'ss A1 is similar to the phenotype observed upon increased splicing at 3'ss A2. Further examination of the role of 5'ss D2 and D3 in the alternative splicing of 3'ss A1 and A2, respectively, is necessary to delineate a role for non-coding exon inclusion in HIV-1 replication.
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Affiliation(s)
- Joshua M Madsen
- Interdisciplinary Program in Molecular Biology, University of Iowa, Iowa City, IA 52242, USA
| | - C Martin Stoltzfus
- Interdisciplinary Program in Molecular Biology, University of Iowa, Iowa City, IA 52242, USA
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
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15
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Soret J, Bakkour N, Maire S, Durand S, Zekri L, Gabut M, Fic W, Divita G, Rivalle C, Dauzonne D, Nguyen CH, Jeanteur P, Tazi J. Selective modification of alternative splicing by indole derivatives that target serine-arginine-rich protein splicing factors. Proc Natl Acad Sci U S A 2005; 102:8764-9. [PMID: 15939885 PMCID: PMC1150812 DOI: 10.1073/pnas.0409829102] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The prevalence of alternative splicing as a target for alterations leading to human genetic disorders makes it highly relevant for therapy. Here we have used in vitro splicing reactions with different splicing reporter constructs to screen 4,000 chemical compounds for their ability to selectively inhibit spliceosome assembly and splicing. We discovered indole derivatives as potent inhibitors of the splicing reaction. Importantly, compounds of this family specifically inhibit exonic splicing enhancer (ESE)-dependent splicing, because they interact directly and selectively with members of the serine-arginine-rich protein family. Treatment of cells expressing reporter constructs with ESE sequences demonstrated that selected indole derivatives mediate inhibition of ESE usage in vivo and prevent early splicing events required for HIV replication. This discovery opens the exciting possibility of a causal pharmacological treatment of aberrant splicing in human genetic disorders and development of new antiviral therapeutic approaches.
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Affiliation(s)
- Johann Soret
- Institut de Génétique Moléculaire de Montpellier, Unité Mixte de Recherche 5535, Centre National de Recherche Scientifique, 1919, Route de Mende, 34293 Montpellier, France
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16
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Bériault V, Clément JF, Lévesque K, Lebel C, Yong X, Chabot B, Cohen EA, Cochrane AW, Rigby WFC, Mouland AJ. A late role for the association of hnRNP A2 with the HIV-1 hnRNP A2 response elements in genomic RNA, Gag, and Vpr localization. J Biol Chem 2004; 279:44141-53. [PMID: 15294897 DOI: 10.1074/jbc.m404691200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two cis-acting RNA trafficking sequences (heterogenous ribonucleoprotein A2 (hnRNP A2)-response elements 1 and 2 or A2RE-1 and A2RE-2) have been identified in HIV-1 vpr and gag mRNAs and were found to confer cytoplasmic RNA trafficking in a murine oligodendrocyte assay. Their activities were assessed during HIV-1 proviral gene expression in COS7 cells. Single point mutations that were shown to severely block RNA trafficking were introduced into each of the A2REs. In both cases, this resulted in a marked decrease in hnRNP A2 binding to HIV-1 genomic RNA in whole cell extracts and hnRNP A2-containing polysomes. This also resulted in an accumulation of HIV-1 genomic RNA in the nucleus and a significant reduction in genomic RNA encapsidation levels. Immunofluorescence analyses revealed altered expression patterns for pr55Gag and particularly that for Vpr. Vpr localization became almost completely nuclear and this was reflected in a significant reduction in virion-associated Vpr levels. These effects coincided with late steps of the viral replication cycle and were not seen at early time points post-transfection. Transcription, splicing, steady state RNA levels, and pr55Gag processing were not affected. On the other hand, viral replication was markedly compromised in A2RE-2 mutant viruses and this correlated with lowered genomic RNA encapsidation levels. These data reveal new insights into the virus-host interactions between hnRNP A2 and the HIV-1 A2REs and their influence on the patterns of HIV-1 gene expression and viral assembly.
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Affiliation(s)
- Véronique Bériault
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute for Medical Research-Sir Mortimer B. Davis Jewish General Hospital, Room 323A, 3755 Côte-Ste-Catherine Road, Montréal, Québec H3T 1E2, Canada
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17
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Ropers D, Ayadi L, Gattoni R, Jacquenet S, Damier L, Branlant C, Stévenin J. Differential effects of the SR proteins 9G8, SC35, ASF/SF2, and SRp40 on the utilization of the A1 to A5 splicing sites of HIV-1 RNA. J Biol Chem 2004; 279:29963-73. [PMID: 15123677 DOI: 10.1074/jbc.m404452200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Splicing is a crucial step for human immunodeficiency virus, type 1 (HIV-1) multiplication; eight acceptor sites are used in competition to produce the vif, vpu, vpr, nef, env, tat, and rev mRNAs. The effects of SR proteins have only been investigated on a limited number of HIV-1 splicing sites by using small HIV-1 RNA pieces. To understand how SR proteins influence the use of HIV-1 splicing sites, we tested the effects of overproduction of individual SR proteins in HeLa cells on the splicing pattern of an HIV-1 RNA that contained all the splicing sites. The steady state levels of the HIV-1 mRNAs produced were quantified by reverse transcriptase-PCR. For interpretation of the data, transcripts containing one or several of the HIV-1 acceptor sites were spliced in vitro in the presence or the absence of one of the tested SR proteins. Both in vivo and in vitro, acceptor sites A2 and A3 were found to be strongly and specifically regulated by SR proteins. ASF/SF2 strongly activates site A2 and to a lesser extent site A1. As a result, upon ASF/SF2 overexpression, the vpr mRNA steady state level is specifically increased. SC35 and SRp40, but not 9G8, strongly activate site A3, and their overexpression ex vivo induces a dramatic accumulation of the tat mRNA, to the detriment of most of the other viral mRNAs. Here we showed by Western blot analysis that the Nef protein synthesis is strongly decreased by overexpression of SC35, SRp40, and ASF/SF2. Finally, activation by ASF/SF2 and 9G8 was found to be independent of the RS domain. This is the first investigation of the effects of variations of individual SR protein concentrations that is performed ex vivo on an RNA containing a complex set of splicing sites.
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Affiliation(s)
- Delphine Ropers
- Laboratoire de Maturation des ARN et Enzymologie Moléculaire, UMR CNRS 7567, Université Henri Poincaré Nancy 1, Boulevard des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy, France
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18
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Jacquenet S, Méreau A, Bilodeau PS, Damier L, Stoltzfus CM, Branlant C. A second exon splicing silencer within human immunodeficiency virus type 1 tat exon 2 represses splicing of Tat mRNA and binds protein hnRNP H. J Biol Chem 2001; 276:40464-75. [PMID: 11526107 DOI: 10.1074/jbc.m104070200] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
An equilibrium between spliced and unspliced primary transcripts is essential for retrovirus multiplication. This equilibrium is maintained by the presence of inefficient splice sites. The A3 3'-splice site of human immunodeficiency virus type I (HIV-1) is required for Tat mRNA production. The infrequent utilization of this splice site has been attributed to the presence of a suboptimal polypyrimidine tract and an exonic splicing silencer (ESS2) in tat exon 2 approximately 60 nucleotides downstream of 3'-splice site A3. Here, using site-directed mutagenesis followed by analysis of splicing in vitro and in HeLa cells, we show that the 5' extremity of tat exon 2 contains a second exonic splicing silencer (ESS2p), which acts to repress splice site A3. The inhibitory property of this exonic silencer was active when inserted downstream of another HIV-1 3'-splice site (A2). Protein hnRNP H binds to this inhibitory element, and two U-to-C substitutions within the ESS2p element cause a decreased hnRNP H affinity with a concomitant increase in splicing efficiency at 3'-splice site A3. This suggests that hnRNP H is directly involved in splicing inhibition. We propose that hnRNP H binds to the HIV-1 ESS2p element and competes with U2AF(35) for binding to the exon sequence flanking 3'-splice site A3. This binding results in the inhibition of splicing at 3'-splice site A3.
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Affiliation(s)
- S Jacquenet
- Laboratoire de Maturation des Acide Ribo-Nucléotidique et Enzymologie Moléculaire, Unité Mixte de Recherche 7567 Université Henri Poincarré-CNRS, Boulevard des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy cedex, France
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19
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Bilodeau PS, Domsic JK, Mayeda A, Krainer AR, Stoltzfus CM. RNA splicing at human immunodeficiency virus type 1 3' splice site A2 is regulated by binding of hnRNP A/B proteins to an exonic splicing silencer element. J Virol 2001; 75:8487-97. [PMID: 11507194 PMCID: PMC115094 DOI: 10.1128/jvi.75.18.8487-8497.2001] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The synthesis of human immunodeficiency virus type 1 (HIV-1) mRNAs is a complex process by which more than 30 different mRNA species are produced by alternative splicing of a single primary RNA transcript. HIV-1 splice sites are used with significantly different efficiencies, resulting in different levels of mRNA species in infected cells. Splicing of Tat mRNA, which is present at relatively low levels in infected cells, is repressed by the presence of exonic splicing silencers (ESS) within the two tat coding exons (ESS2 and ESS3). These ESS elements contain the consensus sequence PyUAG. Here we show that the efficiency of splicing at 3' splice site A2, which is used to generate Vpr mRNA, is also regulated by the presence of an ESS (ESSV), which has sequence homology to ESS2 and ESS3. Mutagenesis of the three PyUAG motifs within ESSV increases splicing at splice site A2, resulting in increased Vpr mRNA levels and reduced skipping of the noncoding exon flanked by A2 and D3. The increase in Vpr mRNA levels and the reduced skipping also occur when splice site D3 is mutated toward the consensus sequence. By in vitro splicing assays, we show that ESSV represses splicing when placed downstream of a heterologous splice site. A1, A1(B), A2, and B1 hnRNPs preferentially bind to ESSV RNA compared to ESSV mutant RNA. Each of these proteins, when added back to HeLa cell nuclear extracts depleted of ESSV-binding factors, is able to restore splicing repression. The results suggest that coordinate repression of HIV-1 RNA splicing is mediated by members of the hnRNP A/B protein family.
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Affiliation(s)
- P S Bilodeau
- Department of Microbiology, University of Iowa, Iowa City, Iowa 52242, USA
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20
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Verhoef K, Bilodeau PS, van Wamel JL, Kjems J, Stoltzfus CM, Berkhout B. Repair of a Rev-minus human immunodeficiency virus type 1 mutant by activation of a cryptic splice site. J Virol 2001; 75:3495-500. [PMID: 11238879 PMCID: PMC114146 DOI: 10.1128/jvi.75.7.3495-3500.2001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We isolated a revertant virus after prolonged culturing of a replication-impaired human immunodeficiency virus type 1 (HIV-1) mutant of which the Rev open reading frame was inactivated by mutation of the AUG translation initiation codon. Sequencing of the tat-rev region of this revertant virus identified a second-site mutation in tat that restored virus replication in the mutant background. This mutation activated a cryptic 5' splice site (ss) that, when used in conjunction with the regular HIV 3' ss #5, fuses the tat and rev reading frames to encode a novel T-Rev fusion protein that rescues Rev function. We also demonstrate an alternative route to indirectly activate this cryptic 5' ss by mutational inactivation of an adjacent exon splicing silencer element.
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Affiliation(s)
- K Verhoef
- Department of Human Retrovirology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
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21
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Jacquenet S, Ropers D, Bilodeau PS, Damier L, Mougin A, Stoltzfus CM, Branlant C. Conserved stem-loop structures in the HIV-1 RNA region containing the A3 3' splice site and its cis-regulatory element: possible involvement in RNA splicing. Nucleic Acids Res 2001; 29:464-78. [PMID: 11139617 PMCID: PMC29680 DOI: 10.1093/nar/29.2.464] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The HIV-1 transcript is alternatively spliced to over 30 different mRNAs. Whether RNA secondary structure can influence HIV-1 RNA alternative splicing has not previously been examined. Here we have determined the secondary structure of the HIV-1/BRU RNA segment, containing the alternative A3, A4a, A4b, A4c and A5 3' splice sites. Site A3, required for tat mRNA production, is contained in the terminal loop of a stem-loop structure (SLS2), which is highly conserved in HIV-1 and related SIVcpz strains. The exon splicing silencer (ESS2) acting on site A3 is located in a long irregular stem-loop structure (SLS3). Two SLS3 domains were protected by nuclear components under splicing condition assays. One contains the A4c branch points and a putative SR protein binding site. The other one is adjacent to ESS2. Unexpectedly, only the 3' A residue of ESS2 was protected. The suboptimal A3 polypyrimidine tract (PPT) is base paired. Using site-directed mutagenesis and transfection of a mini-HIV-1 cDNA into HeLa cells, we found that, in a wild-type PPT context, a mutation of the A3 downstream sequence that reinforced SLS2 stability decreased site A3 utilization. This was not the case with an optimized PPT. Hence, sequence and secondary structure of the PPT may cooperate in limiting site A3 utilization.
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Affiliation(s)
- S Jacquenet
- Laboratoire de Maturation des ARN et Enzymologie Moléculaire, UMR 7567 UHP-CNRS, France
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